The great expansion of the Arabs in the early Middle Ages, often called the "onslaught", lasted from 632 to around 750. In this relatively short period of time, the Arabs conquered huge areas stretching from the peninsula. Iberian, through North Africa, to almost the entire Middle East (except Asia Minor defended by Byzantium), to the borders of today's Pakistan and Afghanistan! Of course, this expansion would not be possible without an efficiently functioning military force. It is assumed that the Arab army around 632 had no more than 15,000 men. However, as early as around 660, their number reached about 100,000 warriors. Only Muslims could serve in this army, which allowed to present the wars waged by Arabs as a fight for the Muslim faith, called jihad. Arab troops, unsurprisingly, were composed of infantry and cavalry. The Arab infantry made use of spears, spears and swords, but also attached considerable importance to the use of bows on the battlefield. The infantry "unit" considered specifically elite was the Mubarizun formation. The Arab cavalry in the period of early conquests is, above all, great light cavalry with very high mobility, resistant to the hardships of marching and doing great on the battlefield. The main weapons of the Arab light cavalry were a spear and a sword. It happened that the Arab commanders placed it behind the formations of their own infantry at the beginning of the battle, but during the fight they used it to attack the opponent's wing or wings. With time, after the experience with the battles with Byzantium and the Sassanid state (7th century), horse archers and heavy armed formations modeled on cataphracts and clibanaria began to appear in the Arab cavalry. The quality of the Arabian troops from the 7th-8th centuries can be seen both in the huge empire that they won, and in battles such as the one on the Yarmuk River in 636.